The air strikes targetted Hajin, a town in a holdout of Daesh group in eastern Syria, killing 26 Daesh family members including 14 children, the Syrian Observatory for Human Rights said.
US-led coalition airstrikes killed 26 civilians including 14 children on Friday in a holdout of the Daesh group in eastern Syria, a Britain-based war monitor said.
"Twenty-six IS (Daesh) family members including 14 children and 9 women were killed in coalition air strikes on Friday morning on the town of Hajin," the Syrian Observatory for Human Rights said.
On Thursday, coalition raids killed another seven civilians in the nearby village of Al Shaafa, Observatory chief Rami Abdel Rahman said.
Both Hajin and Al Shaafa are in a last pocket under Daesh control in the eastern province of Deir Ezzor near the border with Iraq.
A coalition spokesman did not immediately reply for a request for comment.
The coalition has been backing a Kurdish-Arab alliance fighting Daesh in the area.
Daesh overran large swathes of Syria and neighbouring Iraq in 2014, proclaiming a 'caliphate' in land it controlled.
But Daesh has since lost most of it to various offensives in both countries.
In Syria, the group has seen its presence reduced to parts of the vast Badia desert and the pocket in Deir Ezzor.
Since 2014 the US-led coalition has acknowledged direct responsibility for more than 1,100 civilian deaths in Syria and Iraq, but rights groups put the number killed much higher.
The Syrian Observatory for Human Rights says coalition strikes in Syria alone have killed more than 3,300 civilians.
Syria's war has killed more than 360,000 people since it erupted in 2011 with the brutal repression of peaceful anti-government protests.